Friday, January 13, 2017 at 5:14AM
How would you add up the following numbers?
My son started soroban (abacus) lessons this week, so my wife and I have been talking a lot about arithmetic recently.
I told her that although I had been taught to tally up the ones first, I now add up the tens, or round, in order to get a ball park figure.
With rounding, you get:
X < 200
With a multiple choice exam, this will help quickly eliminate answers.
A better way to round that requires a bit of note taking is:
→200 (-5) = 195
I've heard this is the way the Indians are taught to do it. I think Common Core has also tried to introduce a similar method much to the dismay of parents who don't get it.
Adding the tens first you get X > 170.
I've always found this to be a much faster way to do addition and other simple math problems. Apparently, that is also what they do with the soroban. You get an instant "feel" for the answer--it should be about X--then you add in the ones with a few flicks of the beads and come up with the answer.
29→20 + 9
58→50 + 8
72→70 + 2
+36→30 + 6
→170 + 25 = 195
What surprised me, though, is learning how kids here are taught to do math. Apparently, they are instructed to add 29 + 58 first, then add that sum to the next number, 72, then add that to the last number, 36.
29 + 58 + 72 + 36 =
29 + 58 → X + 72 → Y + 36 = the final answer
29 + 58 → 87 + 72 → 159 + 36 = 195
This seems awfully time consuming and all those steps only insure that you're going to fuck up along the way.